| Radioisotopes are radioactive elements that have a different number of
neutrons than their more stable counterparts. The radioactive nature of some of
these atoms have made them extremely useful in the field of nuclear medicine. The
following is a list of some common radionuclides used for diagnostic and therapeutic
purposes, along with the method by which they are produced, their half-lives, and a
few of their medical uses.
Iodine-131 is produced in a nuclear reactor and has a half-life of about
8 days. It is used in the imaging of the thyroid and the treatment of some thyroid
disorders.
Technitium-99m is the result of the slow decay of molybdenum-99.
Nuclear medicine labs receive regular deliveries of molybdenum-99 encased in lead
containers; when the technetium radionuclide is needed, it is washed out of the
container with saline. Technitium-99m has a half-life of six hours and binds easily to
other molecules, making it ideal for a wide variety of diagnostic purposes. This
radiopharmaceutical is used to image such organs as the heart, bones, the lungs, and
the liver.
Thallium-201 is produced in a cyclotron. Its half-life is 73 hours. The molecule's strong chemical resemblance to potassium makes it ideal for imaging myocardial perfusion.
In nuclear medicine, the terms radioisotope, radionuclide, radiopharmaceutical, and tracer are used interchangeably.
Sources:
http://tis.eh.doe.gov/ohre/roadmap/achre/intro_9_4.html
http://www.uic.com.au/nip26.htm
http://chorus.rad.mcw.edu/doc/00391.html
http://www.nidlink.com/~jfromm/nuclear/halflife.htm | 
